1. Field
One or more embodiments of the invention relate to compositions and methods for preparing mesoporous materials from low Si/Al zeolites.
2. Description of Related Art
Previously, methods have been described to introduce mesoporosity into zeolites, for example, in U.S. Patent Application Publication No. 2007/0244347. These zeolites have a high silicon-to-aluminum ratio (“Si/Al”) and low extra-framework content, namely, ultrastable zeolite Y (“USY”) CBV 720 provided by Zeolyst International.
As previously described, this zeolite can be treated in the presence of a pore forming agent (for example, a surfactant) at a controlled pH under a set of certain time and temperature conditions to introduce mesoporosity into the zeolite. Thereafter, the mesostructured material can be treated to remove the pore forming agent (for example by calcination or chemical extraction).
Zeolites used in fluid catalytic cracking (“FCC”) can have larger unit cell sizes than that of CBV 720 (see Table 1). For example, USY zeolite CBV 500, also from Zeolyst, may be a more suitable raw material for FCC applications. Additionally, NH4Y CBV 300, also from Zeolyst, may be suitable for such uses. As shown in Table 1, USY CBV 500 and NH4Y CBV 300 both have larger unit cell sizes, namely 24.53 Å and 24.70 Å, respectively, than USY CBV 720, namely 24.28 Å.
The CBV 500 zeolite contains a significant amount of extra-framework alumina (“EFAL”), due to the leach of some framework alumina (“FA”), as revealed by a decrease in the unit cell size from parent NaY (see Table 1). USY CBV 720, a more stabilized zeolite Y, has a much smaller unit cell size, and a reduced EFAL content, due to an acid wash following a severe stabilization treatment (e.g., steaming). CBV 300 zeolite has a low EFAL content, presumably because it is not subjected to heat treatment.
An EFAL content is the percent total of aluminum that has low extra-framework alumina. From 0-10% can be considered to be a low EFAL content whereas an EFAL content from 25-100% can be considered to be a high EFAL content.
TABLE 1Physicochemical Characteristics of Zeolites Provided by Zeolyst Int'lNaYNH4YUSYUSYCBV 100CBV 300CBV 500CBV 720Unit Cell (Å)24.6524.7024.5324.28EFAL contentLowLowHighLowSi/Al ratio (total)2.62.65.230CationSodiumAmmoniumAmmoniumProton
When the treatment described in previous patent applications to introduce mesoporosity in CBV 720 was used to introduce mesoporosity in CBV 500, no appreciable amount of mesoporosity was observed. In addition, no major change in the physicochemical characteristic of CBV 500 was observed. Similar absences of change were observed for CBV 300 and CBV 100 when subjected to the same treatments.